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WAVES AND TIDES Mrs. Walker – Aquatic Science

WAVES AND TIDES Mrs. Walker – Aquatic Science I. waves : disturbances caused by the movement of energy from a source through some medium (solid, liquid, or gas)

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WAVES AND TIDES Mrs. Walker – Aquatic Science

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  1. WAVES AND TIDES Mrs. Walker – Aquatic Science I. waves: disturbances caused by the movement of energy from a source through some medium (solid, liquid, or gas) 1. energy is transferred from the wind to the water and some parts of the air exert more pressure on the surface than others (bobbing) 2. transfer of energy from water molecule to water molecule in orbit transmits wave energy across surface and causes wave to move 3. as the surface becomes rough, it becomes easier for the wind to grip the water

  2. 4. in an ocean wave, ENERGY moves forward, not the water 5. waves are produced by a GENERATING FORCE and a RESTORING FORCE Generating force or Disturbing force: the energy that causes the wave to form. Waves move away from the disturbing force. 1. wind is most common generating force (wind waves) 2. landslides, volcanic eruptions, faulting, earthquakes, and falling ice can create a tsunami 3. moving ships

  3. B. Restoring force: the force that causes the water to return to its undisturbed surface level 1. surface tension: elastic quality of the surface due to cohesion of water molecules created by hydrogen bonds 2. gravity: restoring force of larger waves

  4. C. Anatomy of a wave: 1. crest: highest part 2. trough: lowest part 3. wave height: vertical distance from bottom of trough to top of crest 4. wavelength: crest to crest or trough to trough 5. period: time it takes for two successive crests to pass a fixed observation point 6. wave speed: wavelength divided by the period

  5. D. Wave motion: 1. the motion of water molecules in wind waves is orbital or circular 2. the wave energy moves to the shore, but the water moves in circles 3. the orbital motion of water particles continues below the surface but decreases with depth ( negligible at a depth below ½ the wave length with less energy of motion found at each depth)

  6. II. Deep water waves/Shallow water waves: A. Deep water waves: (wind waves) move through deeper water more than ½ their wavelength. Wavelength determines the size and shape of the orbital motion B. Shallow water waves: in water that is shallower than1/20 their original wavelength III. Wind Waves: gravity waves formed by the transfer of wind energy into water (small in the Gulf of Mexico due to too much land) A. Wave dimensions are controlled by the winds 1. wind velocity: speed of wind 2. wind duration: length of time wind blows 3. fetch: the uninterrupted distance over which wind blows without significant change in direction

  7. B. Swell formation and dispersion 1. When waves are formed, they move outward. Some waves move faster. Waves will sort themselves into groups with similar wavelengths and speeds. Dispersion: process of wave separation Swell: smooth undulation of ocean caused by dispersion Wave trains: progressing groups of swell with the same origin and wavelength

  8. C. Interference and Rogue Waves: 1. Interference waves: when waves from storms of different speeds and wavelengths overtake and interfere with one another a. constructive interference: when crests and troughs of different waves come together, making a larger wave. b. destructive interference: when crests and troughs cancel each other out, creating smaller waves 2. Rogue waves: unusually high waves that occur when the crests from multiple waves come together. One wave in 1,175 is over three times average height and one in 300,000 is over four times average height. Can instantly sink ships (The Perfect Storm movie)

  9. IV. Surf A. shoaling waves: occur in shallow water. When waves come shallow: 1. wave height increases 2. wave length decreases 3. wave velocity decreases (friction with bottom) 4. wave period stays the same

  10. B. Types of surf: (determined by beach slope) 1. spilling waves: a. foaming at the top b. occur on a gradual slope c. crests slide down the front of the wave d. less than 7 degrees of beach slope 2. plunging waves: a. curl b. good surfing waves c. may form a tube d. 7-15 degrees of beach slope 3. surging waves: a. do not break b. steep c. greater than 15 degrees of beach slope

  11. C. Events leading to the break: 1. When water is less that ½ its wavelength it begins to “feel the bottom” and slow down. 2. Circular motion is interrupted and all energy is pushed up into a crest. 3. Wave becomes too high for its wavelength and can’t support itself 4. Water moves forward as wave breaks

  12. V. Tsunami: A. Caused by sudden movement of water from: 1. Earthquake 2. Landslide 3. Volcanic eruptions 4. Impact of comet of meteorite (rare) B. Considered a shallow water wave (wavelength is very long (130 miles) so ocean reaches ½ this depth C. speeds of up to 500 mph D. Largest ever occurred in Lituya Bay, Alaska due to a landslide. Estimated height was 1500 feet.

  13. V. Tsunami Safety Tips: 1. If in a coastal community at less than 50 feet above sea level and you feel an earthquake – run to high ground! 2. If you see a sudden recession of water – run to high ground! 3. Do not return to low ground for 24 hours.

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